Wireless communication networks are generally capable of providing information on the whereabouts of their subscribers, e.g., to an emergency facility, a traffic surveillance centre or other service unit needing or even requiring such positioning information. In general, the wireless communication networks may sometimes be required to provide and certify the location or position of a subscriber in order to support emergency services and other location dependent or location based services. Various positioning functions are therefore typically employed in the wireless communication networks for locating or positioning UEs connected to base stations in cells of the wireless communication network.
These positioning functions may include simply identifying the cell currently serving a UE of interest, which can provide an accurate enough position when the UE is connected to a base station serving a relatively small cell, but not particularly accurate when connected to a base station serving a larger cell. A more accurate position may further be derived from a used timing advance when the serving cell is known or derived from signal strength measurements on signals from different base station sites, or derived from the used timing advance and signal strength measurements.
The concept of time alignment or timing advance is generally used in wireless communication networks employing time division multiplexing where UEs sharing the same transmit frequency are directed to transmit their signals during allocated timeslots, commonly referred to as TDMA (Time Division Multiplex Access). FIG. 1a illustrates schematically how timing advance is used in a cell covered by a base station BS. Three UEs A, B and C are currently connected to the serving base station BS, and different timeslots 100 are allocated to the UEs such that UEs A, B, and C are directed to transmit signals “A,” “B” and “C” in successive timeslots 100, respectively, as indicated in FIG. 1a. The UEs A-C are thus synchronised with BS to allow for proper timing of the transmission and reception of signals.
In this example, UEs A and C are located relatively close to BS, while the UE B is located at a greater distance from BS. As a result, the signals from UEs A and C will arrive basically “in time” to BS while the signals from the UE B would arrive somewhat late due to propagation delays, thus not exactly fitting into the allocated timeslot when received at BS, which could cause interference due to overlap with signals from the UE C in this case. In order to avoid such interference, BS orders the UE B to transmit its signals somewhat earlier by a parameter called Timing Advance (TA). This mechanism is generally referred to as time alignment. Thus, by adjusting the timing of transmissions from the UE B in this way, the signals will arrive properly at BS in the allocated timeslot as indicated in FIG. 1a. 
Although the parameter TA was originally conceived to adjust UE transmissions to fit into a timeslot scheme at the receiving base station, TA has been frequently utilised to provide location information as well. As the propagation speed of radio signals is known to equal the speed of light C, the TA used by a specific UE further implies the distance D between that UE and the serving base station as D=½C×TA. According to 3rd Generation Partnership Project (3GPP), TA is specified as an integer between 0 and 63 representing time steps in the interval 0 μs through 232 μs, each step thus representing approximately 3.7 μs which corresponds to 553 meters of signal propagation. The location of a UE can thus be estimated by knowing the location of the serving base station and the TA used. In many wireless systems, the base station's location is basically given by a parameter “Cell Global Identity” (CGI) providing the coordinates of the base station.
FIG. 1b illustrates that when a UE, not shown, is directed by a serving base station BS to use a specific timing advance value TA to adjust its transmissions, that TA value can further be used to calculate an expected UE distance from BS as being within a potential position area P at a distance of TA×553 meters from BS, according to 3GPP. If BS covers 360°, i.e., an omni cell, the UE is presumably located somewhere within a circle area or ring P(Omni), while if BS covers a sector less than 360°, i.e., a sector cell, the UE can be somewhere within a circle sector area P(Sector), as illustrated in FIG. 1b. For example, if TA=10, the UE is expected to be located at a distance of around 5.5 kilometers from the base station. Since TA is specified in 3GPP according to predefined integers, the expected UE/base station distance can be determined within an uncertainty interval of 553 meters.
Utilising the CGI/TA information for positioning is particularly attractive since it is promptly available at the serving base station or at a base station controller BSC, and no further measurements nor added functionality in UEs are necessary. The above positioning method is frequently used in Global System for Mobile Communications (GSM) and other similar mobile systems using timing adjustment. For instance, the concept of cell ID and timing information as discussed before can also be equally applied in other radio access technologies, e.g., Wideband Code Division Multiple Access (WCDMA) and Long Term Evolution (LTE), which have a very similar mechanism of “cell” and “timing compensation” as GSM.
Take an LTE system as an example, as illustrated in FIG. 2a, an Evolved Serving Mobile Location Centre (E-SMLC) is able to obtain timing information (UE reception-transmission) from the UE which is shown as a handset via an LTE Positioning Protocol (LPP) interface or from eNB (evolved Node B, a particular form of a base station) through a Mobility Management Entity (MME) via an LTE Positioning Protocol A (LPPa) interface. By using timing information in the enhanced cell identifier (ECID) method, the E-SMLC is capable of determining the position of the UE. However, the position determined in this manner gives rise to some problems in terms of accuracy and overhead.
It is known that the timing information (more specifically, the timing value) reported by the UE through the LPP interface is relatively unreliable since remarkable uncompensated additional delay as illustrated in FIG. 2b exists between the antenna and eNB baseband possibly due to the cabling, a deployed Radio Remote Unit (RRU), etc. This kind of delay may vary from site to site and could reach microsecond level or tens of microsecond level which corresponds to hundreds of meters or several kilometers in terms of the location error, which may be unacceptable and may render the positioning less than optimal or sometimes inaccurate.
In order to eliminate or shorten this delay and obtain a reasonably good accuracy for the positioning, the eNB would offset the timing value with the estimated delay prior to sending the timing value to the E-SMLC via the LPPa interface. Accordingly, the E-SMLC needs to interact with the eNB through the LPPa interface for reliable timing based positioning. However, the LPP positioning associated with the LPPa signaling might not be expected by the 3GPP standards.
That being the case, for each LPP ECID positioning session, the E-SMLC will be forced to trigger an LPPa session for timing measurement due to instability of the LPP timing measurement. This would inevitably result in the lengthened response time and additional network resources for signaling transmissions involving the MME and eNB as illustrated in FIG. 2a. 
Further, a User Plane location server (e.g., SLP in FIG. 2b) which is also capable of positioning the UE, can only use the LPP over the User Location Protocol (ULP) to request the timing value from the UE rather than using the LPPa since the LPPa is only for the Control Plane. Due to absence of the LPPa interface, the accuracy achieved by the SLP in positioning would be degraded.